With recent technological advancements in computer and wireless communications, mobile wireless computing has seen increasingly widespread use and application. Not constrained by wires, users with mobile computing devices can move around freely at their convenience, and may often need to communicate with each other in circumstances where there is no fixed infrastructure. In such cases, they can form a mobile ad hoc network (MANET) or mobile wireless mesh network. A mobile wireless mesh network is an autonomous system of wireless mobile routers (and associated hosts), which can move randomly and re-organize themselves into an arbitrary network without any underlying backbone and infrastructure.
Besides mobile wireless mesh networks, recently, interesting commercial applications of fixed wireless mesh networks have also emerged. One example of such a commercial application is “community wireless networks,” which are used to provide broadband Internet access to communities that previously did not have such access. In these fixed “community wireless networks”, each wireless router in the network not only provides Internet access for attached users, but also becomes part of the network infrastructure and can route data through the wireless mesh network to its destination. A routed wireless mesh network is highly flexible and inherently fault-tolerant. It simplifies line-of-sight problems and extends the reach and coverage of the network with a minimal amount of network infrastructure and interconnection costs.
There are also hybrid wireless mesh networks where some mesh routers are mobile and the others are not. In whatever cases (whether mobile or fixed or hybrid), wireless mesh networks have some salient characteristics, such as: highly dynamic, autonomous, peer-to-peer, multi-hop, often limited bandwidth and computing power etc. The wireless mesh networks are highly dynamic for two reasons: First, the routers themselves may move (e.g. in mobile or hybrid wireless mesh networks), causing fast topological changes. Second, even if the routers themselves don't move (e.g. in fixed wireless mesh networks), the radio link qualities can change very quickly because of interference, geographical and environmental factors etc. The traditional routing protocols (e.g. OSPF, RIP), designed for wired infrastructures, can not handle such rapid changes. Many of the ad hoc routing protocols (e.g. AODV), lack the ability to flexibly adapt to the radio link quality changes.
Voice over Internet Protocol (VOIP) is expected to be a key application in wireless mesh networks. VoIP enables voice telephone calls to be made over existing Internet infrastructure by digitizing sound into standard Internet Protocol data packets. This stream of data travels over the standard Internet infrastructure to its destination. If the destination is another VoIP device, the digitized data stream is converted into sound on the device; if the destination is a traditional telephone, the stream is converted into an analog signal by a special gateway device and then travels through traditional telephone lines. This is a potentially market disruptive application, as it allows wireless devices to make telephone calls without requiring access to traditional cell-phone based infrastructure.
VoIP requires certain quality of service guarantees from the Internet infrastructure in order to avoid interruptions or dropouts in continuous voice signals. During the initiation of a call, the access points in a VoIP network will ensure that there is sufficient capacity within the network to ensure continuous, smooth voice transmission. The decision as to whether a network can support a newly initiated or incoming VoIP call is called Call Admission Control (CAC). Call Admission Control is complicated by the dynamically changing nature of the network. In particular, mobile mesh networks encounter constantly changing structure as devices and access points move in to, out of, and across the mesh.
The method and system described below enable access points in a mesh network to act as a Session Initiation Protocol (SIP) proxy for relaying SIP messages between user agents. According to the invention, location and availability information for an access point is provided as an additional header field in standard SIP call requests and responses. The information in this header can then be used to form either a centralized or distributed CAC system. In the distributed system, the Call Capacity Information (CCI) may be propagated in two ways: by piggybacking that information on an existing routing protocol's regular update or by a trigger update mechanism.